EMUdesign (1).doc - SYSTEMS FOR MARS EMU DESIGN George William Herbert INTRODUCTION There are five primary justifications for manned extravehicular

EMUdesign (1).doc - SYSTEMS FOR MARS EMU DESIGN George...

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SYSTEMS FOR MARS EMU DESIGN George William Herbert INTRODUCTION There are five primary justifications for manned extravehicular surface operations on Mars: Geological exploration, Exobiology, other Mars Science, Base Construction, and Maintenance. Accomplishing these first three goals is the primary intent of any manned Mars mission. The EVA Systems, the Space Suit and Portable Life Support System (PLSS) together known as the EMU or Extravehicular Mobility Unit, are required for accomplishing those surface operations goals. To the extent possible, those goals should drive the concept and design of Mars EVA systems, to maximize the successful returns from any manned Mars mission. This paper discusses a portion of the results of a 1989-1991 study performed on issues involved in designing Mars EVA systems. It concentrates on technology and systems issues involved in Mars EMU design. EMU REQUIREMENTS An EMU must provide a safe, comfortable environment for its occupant, maintaining atmospheric pressure, temperature, acceptable oxygen and CO2 levels, protect from contamination (physical and biological), handle other metabolic wastes, and provide physical protection from tears and punctures1. To maximize useful work per EVA, 8 hour endurance is required. A 30 minute backup life support system should be installed to maintain current safety levels. The EMU should provide constant communications with other suits, rovers, or bases. The occupant should be able to walk at 6.5 km/hr and drive a rover while wearing the EMU. The EMU must provide all of these in a package which is light and mobile enough to allow the primary EVA goals to be accomplished as easily as possible. EMU Weight The Mars environment presents a unique challenge to EVA operations: significant surface gravity. Its surface gravity is 0.36 earth's. The moon, the only other surface EVA location to date, has less than half this gravity. EMU systems have traditionally been quite massive. The Apollo suits massed 38 kg, with a 62 kg PLSS for a total of 100 kg. A total EMU mass of 100 kg would be overwhelming on the Mars surface; obviously system mass must be reduced. The baseline rule determined by the study group was that the Mars EMU perceived weight (mass x gravity) on Mars should not exceed the Apollo EMU perceived weight on the moon. The target system mass was therefore determined to be 45 kg. This massively lower allowable EMU mass requires a fundamental rethinking of suit design concepts. PASSIVE EMU COOLING Around 14 kg of the Apollo EMU's mass is in its thermal control systems. This is a particularly attractive area for reduction of mass because the Mars atmosphere provides a cool sink which can be used to passively cool an EMU. The general concept behind passive cooling is to design a suit such that the thermal balance of heat generated metabolically and absorbed from sunlight is balanced by convective and radiative losses to the Mars atmosphere, maintaining a stable and comfortable temperature for the user.
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